Many studies have linked poor sleep -- whether from insomnia or working the night shift -- to weight gain and health conditions like type 2 diabetes. But that type of research leaves open the question of whether sleep loss itself is to blame.

A growing number of lab studies, zeroing in on the effects of sleep deprivation, suggest the answer is "yes." The new research adds to the evidence.

"We need mechanistic studies to understand the effects of sleep loss," said lead researcher Dr. Jonathan Cedernaes, a research associate at Northwestern University, in Chicago.

Cedernaes said studies have shown, for example, that sleep loss can change a range of markers in the blood -- including blood sugar, hormone levels and various byproducts of metabolism.

For the new study, his team dug into the effects within fat and muscle tissue -- looking at how gene activity and protein levels in those tissues changed after a sleepless night.

The investigators found that in 15 young, healthy men, one night of sleep loss triggered changes that favored fat storage and muscle breakdown.

"This doesn't mean you should be alarmed by one night of sleep loss," Cedernaes stressed. But, he added, the study raises the question of what would happen if poor sleep becomes a regular pattern.

The findings were published online Aug. 22 in the journal Science Advances.

A sleep researcher who was not involved in the study called the findings "extremely important."

"The finding that skeletal muscle proteins decrease, and [fat-promoting] proteins increase, in response to sleep loss is a novel mechanism by which sleep loss may promote obesity and weight gain," said Josiane Broussard, an assistant professor at Colorado State University, in Fort Collins.

With any lab study, however, it's not clear how well the artificial conditions reflect real life.

Dr. Eva Szentirmai, an associate professor at Washington State University, in Spokane, who studies sleep and metabolism, said, "We don't know if you would observe similar tissue-specific changes during long-term, habitual sleep loss -- which is common in our society."

In addition, the experiment did not fully capture what it's like to work at night, for example.

The volunteers spent two nights in the sleep lab: on one night, they could sleep for up to 8.5 hours; on the other night, they were kept awake all night, but had to stay in bed.

The point, Cedernaes explained, was to isolate the metabolic effects of sleep loss itself.

But in real life, someone working the night shift would be physically and mentally active, eating and going about life during the part of the day when humans normally sleep.

In addition, Szentirmai pointed out, they would be exposed to irregular lighting patterns. And changes in light and eating patterns may directly affect "muscle protein balance," she said.

So, she noted, it's possible that night-shift work could add to any negative effects of sleep loss on muscle and fat tissue.

What about those who simply stay up late and don't get enough sleep? Szentirmai said studies have shown that those people tend to gain more weight over time, and have higher risks of obesity, versus well-rested people.

But, she added, those studies don't prove cause and effect.

Cedernaes pointed to the bigger picture: Sleep has an important impact on overall health, and people need to get enough of it. Individuals vary in how much sleep they need, he said. But in general, it's recommended that adults get seven to nine hours each night.

If you work at night and must sleep irregular hours, Cedernaes said, try to be particularly vigilant about other lifestyle habits -- like eating a healthy diet and getting regular exercise.

According to Broussard, research like this could eventually help shift workers and others who cannot avoid irregular sleep hours. If researchers understand exactly how sleep disruptions affect the body, she said, they might identify specific ways to counter those effects.

The list of medical terms above are retrieved automatically from the article.

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